This article explores the legal geography of family law in post-colonial Muslim societies. Drawing on a case study in Aceh, Indonesia, it analyses how diverse Islamic leaders were able to influence a controversial administrative reform of family law in the reconstruction period after the 2004 Indian Ocean tsunami. I argue that while Islamic leaders are important stakeholders in law-making in Aceh, they are not a unified collective: rather they mobilise a variety of different practices of legal reasoning to bring legal constructions into agreement. Using the case of an administrative reform of marriage registration, a subordinate regulation in family law, I describe how Islamic leaders deliberate about social issues across their different schools and factions in order to address contemporary problems, while at the same time, mobilising interpretations of Islamic texts as a meaningful tradition for law-making. The analysis builds on ethnographic fieldwork in Aceh, in particular qualitative interviews with civil servants working in the provincial government: Muslim actors, civil rights activists, national experts, international experts, politicians, and diplomats. The article provides impetus to debates in legal geography by illuminating the negotiations of legal reasoning in Muslim societies to make Islamic law, customary law and state-centric state administration compatible.